Homopolar electrical machines



Feb. 24, 1970 l A. D. APPLETON n 3,497,739

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' HoMoPoLAR ELECTRICAL MACHINES Filed Dec. 26, 1967 3 Sheets-Sheet 2Feb. 24, A1970 A. D. APPLETON HOMOPOLAR ELECTRI GAL MACHINES Filed Deo.26, 19e? 5 Sheets-Sheet 3 v, n@ Mm ,4J Z d. a EP-l.. ...Mln-...Ilm w 2!I. |l. in l. Il i i ...n In i iinlh E iin United States PatentHOMOPOLAR ELECTRICAL MACHINES Anthony D. Appleton, Newcastle-upon-Tyne,England, as-

signor to The International Research & Development Company Limited,Newcastle-upon-Tyne, England Filed Dec. 26, 1967, Ser. No. 693,548Claims priority, application Great Britain, Jan. 3, 1967, 371/67; Jan.26, 1967, 3,981/67, 3,982/67 Int. Cl. H02k 31/02 U.S. Cl. 310-178 7Claims ABSTRACT OF THE DISCLOSURE A homopolar electrical machine inwhich the rotor has a plurality of mutually-insulated conducting pathsand sets of stationary brushes engaging contact segments at the ends ofthe paths have a spacing which is a multiple of the contact segmentspacing and are interconnected to provide a series connection between anumber of the con ducting paths. The rotor is of disc form and isprovided with a set of auxiliary conducting paths arranged in a. planeparallel to the main conducting paths and each main path has a separateauxiliary path connected in series with it.

This invention relates to homopolar electrical machines.

Such machines usually comprise a rotating disc or drum havingelectrically conducting paths thereon and operate at low voltage andhigh current. A machine having a disc or drum construction is describedin our co-pending British patent application No. 1-0,062/65.

The voltage and power output of such machines is a direct function ofthe number of discs or drums used and the operating voltage can beincreased by connecting a number of discs or drums electrically inseries.

The need to use a number of discs or drums connected lin series for suchpurposes adds to the cost and comconducting path being associated with afirst and second segment, first and second sets of brushes are mountedto co-operate with the first and second contact segmentsrespectively,the centre to centre spacing of the brushesin 'the two sets is the sameand is two or more times the spacing of the segments of the associatedset, the brushes are dimensioned to bridge adjacent contact segments inpassing from one to thernext, and brushes of the first set areelectrically connected to brushes of the second set to effect a seriesconnection between terminals for connection to an external circuit ofthose conducting paths whose associated contact segments are both incontact with the brushes, the arrangement being such that at certainpositions of the rotor some conducting paths are connected in serieswhile between each pair of series-connected paths there is at least onepath which is not seriesconnected.

The brushes may be solid brushes, for example, con- .Ventional graphitebrushes, or formed of metal wire or strip, or may be constructed to makea liquid contact with the segments.

The brushes of the two sets may be electrically connected by leads whichpass radially from a brush co-operating with the outer set of contactsegments to a position adjacent the inner set of segments and then passin a cir- ICC cumferential direction to a brush co-operating with theinner set of segments.

In a preferred construction a disc-type rotor comprises a support on oneside of which the conducting paths and the sets of first and secondcontact segments are mounted and on the other side of which for each ofthe main conducting paths there is an auxiliary conducting path withassociated third and fourth contact segments for co-operation `withbrushes of third and fourth sets which correspond in number to those ofthe first and second sets, each of the main conducting paths beingelectrically connected between a first segment and a third segment andeach of the auxiliary conducting paths being electrically connectedbetween a fourth segment and a second segment, and each of the brushesof the third set being electrically connected to a corresponding brushof the fourth set to connect the third and fourth segments, associatedwith an auxiliary conducting path when the first and second segmentsassociated with the corresponding main conducting path are in engagementwith brushes of the rst and second sets, whereby the auxiliary path isplaced in series with the main path between the brushes of the rst andsecond sets.

The invention will now be described in more detail with the aid ofexamples illustrated in the accompanying drawings, in which:

FIGURES l and 2 are schematic diagrams of the electrical arrangement ofa rotor of a machine in accordance with the invention for two positionsof the rotor,

FIGURE 3 is a perspective view of part of a disc-type rotor with itsbrushes, some elements being omitted for clarity,

FIGURE 4 is a diagram of an alternative form of disctype rotor,

FIGURE 5 is a view similar to that of FIG. 3 of a further form ofdisc-type rotor in accordance with the invention,

FIGURE 6 shows the electrical connections of the rotor of FIG. 5 indiagrammatic form similar to the diagrams of In FIGS. 1 and 2 individualconducting paths of a disctype rotor are shown as strips 1a to 1jrunning between a first set of contact segments 2a to 2 j and a secondset of contact segments 3a to 3j. In the disc-type rotor the conductingpaths extend radially and the dimension A represents the outercircumference of the disc and the dimension B represents the innercircumference. For convenience of explanation the strips 1a and 1i,which in a practical construction would be adjacent, have been shownagain at each end of the series. f

A set of brushes 5a to Se are arranged to co-operate with the contactsegments 2a to 2j and a second set of brushes 6a to 6e are arranged toco-operate with the contact segments 3a to 3]'. The brushes of the `twosets are interconnected by leads 7. The pitch PB of the brushes is twicethe pitch Ps of the contact segments. Thus with the fixed brush sets andthe rotating contact segments in the relative positions shown in FIG. lalternate conducting strips 1a, 1c, 1e, 1g and 1i have their contactsegments in engagement with brushes 5a and 6a, 5b and 6b, 5c and 6c, 5dand 6d, 5e and 6e respectively and by virtue of the leads 7 connectingbrushes 5a and 6b, 5b and 6c, and so on, are connected in series betweenterminals T1 and T2 which are connected to the external circuit. At thistime the intervening conducting strips 1b, 1d, andso on are not incontact with any brush and are thus not part of the operating circuit.

When the rotor moves on to the position shown in FIG. 2 each brushbridges two contact segments and, for example, conducting strips 1a and1b are connected in parallel between brushes 5a and 6a by way of therespective contact segments 2a, 3a and 2b, 3b. The voltage is unalteredbut the current is shared between the two strips which are connected inseries with other pairs of strips 1c and 1d, 1e and 1f, etc. It will beapparent that upon further rotation of the rotor a position similar tothat of FIG. l is reached in which strips 1b, 1d, 1f, 1h and 1]' areconnected in series and strips 1a, 1c, 1e, 1g and 1i are disconnected.

The connections T1 and T2 to the rotor supply power if the rotor formspart of a homopolar motor, or remove power if the rotor forms part of ahomopolar generator.

If for the purpose of explanation it is assumed that an EMF` isgenerated in the conducting paths in a radially inward direction andthat the EMF generated in each conductor is E volts, then for the rotorposition shown sharting at T1 we have zero voltage on brush 5d, E voltson brushes 6d and 5c 2E volts on brushes 6c and 5b, 3E volts on brushes6b and 5a, 4E volts on brushes 6a and 5e and 5E volts on brush 6e whichis connected to output terminal T2. The output voltage for the exampleshown is thus ve times the voltage generated in each conducting path.the EMFs generated in the conducting paths 1b, 1d, 1f, and 1h do notcontribute to the output. V The EMF generated is a direct function ofthe number of conducting paths connected in series and as a consequenceof connecting the conducting paths in the manner shown the voltage atwhich the machine operates can be varied in a relatively simple andcheaper manner compared with the previous arrangements in which suchvoltage increases have been obtained by increasing the number of discsor drums. The arrangement in accordance with the invention does notpreclude the use of a number of discs but for a given voltage output theduplication of discs is reduced compared with previous arrangements. Thenumber of conducting paths which can be connected in series is limitedonly by practical constructural considerations.

FIG. 3 shows a double disc-type rotor having the conducting paths of thetwo discs connected in series. A pair of disc-shaped assemblies and 11of conducting paths are mounted back to back on a common insulatingsupport disc 12 to form a rotor which in conventional manner is disposedin a magnetic lield lwhose lines of force are generally parallel to theaxis of rotation of the rotor and are thus cut by the radially extendingconducting paths of the rotor as the rotor rotates. The assemblies 10and 11 each have an inner set of mutually insulated contact segments 10aand 11a, respectively, and an outer set of mutually insulated contactsegments 10b and 11b, respectively, and between each pair of oppositecontact seg.- ments 10a and 10b is a radially-extending conducting path10c while between each pair of opposite contact segments 11a and 11b isa radially-extending conducting path 11C. The insulation betweenadjacent contact segments is shown at 13. The conducting paths may be ofcopper or an alloy thereof. 'Ihe conducting paths 10c and 11C aresector-shaped but they could have other shapes. They could for examplebe in the form of rods or bars or parallel-sided strips. It will be seenthat each contact segment extends transversely to the plane of the discand the segments of each set form a cylindrical surface for engagementby the brushes. Solid burshes of electrical-conducting material such ascarbon or graphite are arranged in sliding contact with the contactsegments of each set, brushes 14 contacting the contact segments 10a,brushes 15 the segments 10b, brushes 16 the segments 11a and brushes 17the segments 11b.

In the Iform illustrated the brush pitch or spacing `between the brushesis twice the pitch or spacing of the contact segments, but it could be agreater multiple so that in a position of the rotor corresponding tothat shown there would be more than one intervening segment between apair of adjacent brushes.

The brushes 14 and 15 are interconnected by leads 7 (only one of whichis shown) in the manner described with reference to FIGS. 1 and 2. Theleads 7 pass radially inwards from the brushes 15 for a large proportionof their length and close to the brushes 14 they are carried roundcircumferentially to the appropriate brush, as at 7a. Such anarrangement reduces the effect of armature reaction due to currentflowing in a circumferential direction. i

The connections between the brushes 16 and 17 are similarly arranged sothat a number of the conducting paths 11c are connected in series. Theterminal lead 18 connected to one of the brushes 14 is connected to theterminal lead 19 connected to one of the brushes 16 and this places theconducting paths on the two sides of the rotor in series between aterminal lead 20 connected to one of the brushes 15 and a terminal lead21 connected to one of the brushes 17.

FIG. 4 shows schematically an alternative form of disc type rotor inwhich the conducting paths between outer contact segments 22 and innercontact segments 23 are -formed by rods or spokes 24.

The inner segments 23 are made longer in the axial direction than theouter segments 22 in order to provide the necessary contact area forcurrent collection. The rods 24 may be carried on a support. If desiredseveral rods, bars or strips can be associated with a pair of contactsegments to constitute a single conducting path.

Whilst in the embodiment of FIG. 3 the contact segments are formed bybending the strips which form the conducting paths, they could beseparate members bonded to the conducting strips.

The brushes used to transfer current may be conventional graphite'brushes or take the form of an electrically conducting metal strip orwire.

The conducting paths may themselves constitute the rotor or they may bemountedon a supporting member.

FIGS. 5 and 6 illustrate an alternative form of disc-type rotor in whichinstead of having a series-connected set of conducting paths on one sideconnected in series with a series-connected set of paths on the otherside of the rotor, each conducting path on one side is connected inseries with an auxiliary conducting path on the other side. This isachieved by the use of interconnected sets of stationary brushes andconnections through the supporting disc ofthe rotor.

The rotor shown in FIG. 5 has a supporting disc 25 on one side of whichare mounted a set of sector-shaped main conducting paths 26 and on theother side of which are mounted a set of sector-shaped auxiliaryconducting paths 27. The conducting paths 26 are each individuallyconnected to one of a first set of contact'segments 28 arranged at theinner periphery of the conducting paths 26. A second set of contactsegments 29 are arranged around the outer periphery of the conductingpaths 26 but are insulated therefrom by an insulating ring 30. Brushes31 and 32 co-operate with the contact segments 28 and 29, respectively,and are interconnected by leads 33 in the manner previously describedwith reference to FIGS. 1 to 3.

On the other side of the disc 25 a third set of contact segments 34 arearranged around the other periphery and insulated from the conductingpaths 27 by an insulating ring 35. Each of the conducting paths 26 onone side of the disc is connected to an individual one of the contactsegments 34 on the other side of the disc by a pin 36 which passesthrough an insulating bush 37 in the contact segment 29, through aclearance hole in the disc 25 and into an insulating bush (not shown) inthe correponding conducting path 27. The pin 36, which is in threadedand electrically conducting engagement 'with the conducting path 26 andthe contact segment 34 and is in threaded engagement in the insulatingbushes in the conducting path 27 and contact segment 29, serves for themechanical assembly of the rotor as well as the required electricalconnection. In a similar manner each of the conducting paths 27 isconnected to an individual one of the contact segments 29 by a pin 38which serves for mechanical assembly and electrical connection, passesthrough the disc 2S and engages an insulating bush 39 in the conductingpath ,26.

Each of the conducting paths 27 is directly electrically connected to anindividual segment of a fourth set of contact segments 40 at the innerperiphery of the rotor. Sets of brushes 41 and 42 are arranged toco-operate with the contact segments 34 and 40, respectively, and eachbrush of one set is connected to the corresponding brush of the otherset by a radially-extending lead 43.

The electrical layout of the rotor of FIG. 5 is shown schematically inFIG. -6. It will be seen that the upper half of FIG. 6 resembles FIG. lin the arrangement of the brushes 31 and 32 and contact segments 28 and29v with the connecting leads 33 between the brushes to produce a seriesconnection of conducting paths between terminals T1 and T2. Howeverbetween each of the conducting paths 26 and the associated contactsegment 29 an auxiliary conducting path 27 is connected by way of a pin36, a contact segment 34, brushes 41 and 42 interconnected by a lead 43,and a contact segment 40, and by way of a pin 38 connecting theauxiliary path 27 to the contact segment 29.

To ensure continuity of current flow the brushes must be wide enough orthe number of brushes on a given segment must be sufficient to ensurethat a portion of a brush is always in contact with a slip-ring segment.

Whilst carbon brushes have been described the brushes could be in theform of metal strips or have other suitable forms.

The contact segments are individually insulated from one another.

The magnetic eld may be generated by electromagnets and a magnetic coreor by means of a superconducting coil.

I claim:

1. A homopolar electrical machine having a disc-type rotor carrying aplurality of radially extending conducting paths disposed around therotor and a stator comprising means for generating a magnetic fieldwhich is cut by the conducting paths as the rotor rotates wherein therotor has a set of rst contact segments at the outer periphery of thedisc and a second set of contact segments at the inner periphery of thedisc, each set forming a cylindrical surface for contact by brushes,each conducting path being associated with a rst and second segment, rstand second sets of brushes are mounted to cooperate with the cylindricalsurfaces formed by the rst and second sets of contact segmentsrespectively, the center to center spacing of the brushes in the twosets is the same and is two or more times the spacing of the segments ofthe associated set, the brushes are dimensioned to bridge adjacentcontact segments in passing from one to the next, and brushes of the rstset are electrically connected to brushes of the second set to effect aseries connection between terminals for connection to an externalcircuit of those conducting paths whose associated contact segments areboth in contact with the brushes, the arrangement being such that atcertain positions of the rotor some conducting paths are connected inseries while between each pair of series-connected paths there is atleast one path which is not series-connected.

2. A homopolar machine as claimed in claim 1 wherein said first set ofbrushes is in engagement with the radial inner face of said irst contactsegments.

3. A homopolar machine as claimed in claim 1 in which the brushes of thetwo sets are electrically connected by leads which pass radially from abrush co-operating with the radially outer set of contact segments to aposition adjacent the radially inner set of segments and then pass in acircumferential direction to a brush co-operating with the radiallyinner set of segments.

4. A homopolar machine as claimed in claim 1 in which the rotor has twosets of conducting paths disposed on opposite sides of a suport disc andthe arrangement 6 is such that for a given position of the rotor each ofthe series-connected paths of one set is connected in series with acorresponding conducting path of the other set and the series-connectedpairs of conductors thus formed are themselves connected in series.

5. A homopolar machine as claimed in claim 1 in which the rotorcomprises a support disc on one side of which the conducting pat-hs andthe first and second sets of contact segments are mounted and on theother side of which for each of the main conducting paths there is anauxiliary conducting path with associated third and fourth contactsegments for co-operation with brushes of third and fourth sets whichcorrespond in number to those of the rst and second sets, each of themain conducting pat-hs being electrically connected between a firstsegment and a third segment and each of the auxiliary conducting pathsbeing electrically connected between a fourth segment and a secondsegment, and each of the brushes of the third set being electricallyconnected to a corresponding brush of the fourth set to connect thethird and fourth segments associated with an auxiliary conducting pathwhen the first and second segments associated with the correspondingmain conducting path are in engagement with brushes of the rst andsecond sets, whereby the auxiliary path is placed in series with themain path between the brushes of the first and second sets.

6. A homopolar machine as claimed in claim 1 in which the rotorcomprises a support disc on each side of which are mounted a group ofconducting paths and associated contact segments, separate sets ofbrushes being provided for connecting in series the conducting paths ofthe two groups and the two sets of brushes being connected in series.

7. A homopolar electrical machine having a disc-type rotor comprising asupport carrying on one side a plurality of conducting paths disposedaround the rotor and a stator comprising means for generating a magneticfield Which is cut by the conducting paths as the rotor rotates whereinthe rotor has a set of rst contact segments and a set 0f second contactsegments, each conducting path being associated with a rst and secondsegment, rst and second sets of brushes are mounted to cooperate withthe rst and second contact segments respectively, the center to centerspacing of the brushes in the two sets is the same and is two or moretimes the spacing of the segments Of the associated set, the brushes aredimensioned to bridge adjacent contact segments in passing from one tothe next, and brushes of the first set are electrically connected tobrushes of the second set to effect a series connection betweenterminals for connection to an external circuit of those conductingpaths whose associated contact segments are both in contact with thebrushes, the arrangement being such that at certain positions of therotor some conducting paths are connected in series while between eachpair of series-connected paths there is at least one path which is notseries-connected, the support carrying on the other side, for each ofthe main conducting paths, and auxiliary conducting path with associatedthird and fourth contact segments for cooperation with brushes of thirdand fourth sets which correspond in number to those of the iirst andsecond sets, each of the main conducting paths being electricallyconnected between a rst segment and a third segment and each of theauxiliary conducting paths being electrically connected between a fourthsegment and a second segment, and each of the brushes of the third setbeing electrically connected to a corresponding brush of the fourth setto connect the third and fourth segments associated with an auxiliaryconducting path when the first and second segments associated with thecorresponding main conducting path are in engagement with brushes of thefirst and second sets, whereby the auxiliary path is placed in serieswith the main path between the brushes of the first and second sets.

(References on following page) References Cited OTHER REFERENCES UNITEDSTATES PATENTS Steinmetz lublication, TK2181.57, Theory & Calcula-1223094 4/1917 Neuland Hu 310 178` tlon of Electrlcal Apparatus; pp.450-458. 1,255,838 2/1918 Knoll 310-178 Sykes 5 Pnmary Examlner2,261,684 11/ 1941 Jones 31o-178 R. SKUDY, Asslstant Examiner 3,187,2126/1965 Sears 310--178 Y U S C1 .X R FOREIGN PATENTS 310 268 290,5921/1944 Germany. 10

